Proper alignment of the barrel and receiver in firearms is an important factor bearing upon the reliability, safety, and accuracy of the firearm. It is desirable for the barrel and receiver to be properly aligned and securely joined in such a manner that the two joined components are nearly as rigid as a single member. Prior methods of, and means for, attaching the barrel and receiver include pinning or bolting the barrel to the receiver by means of an external fastener, and attaching the barrel to the receiver by threading. Pinning and bolting do not produce a union that approaches the theoretical rigidity of a single member, thus limiting the accuracy of the firearm. Threading is not practical in firearms adapted to fire rimmed ammunition. Accordingly, a need remains for an improved method, and means for, attaching the barrel of a firearm to the receiver.
A further need exists for a receiver system capable of accepting multiple lengths of barrels or different calibers on the same receiver platform. In prior art, the ability to change calibers or barrel lengths could only be achieved by swapping the entire upper receiver or by changing the barrels at armorer level rather than in the field.
Not only is a means for quick barrel changeover desirable, a barrel changeover means not requiring the use of any tools is especially desirable. Further, a modular receiver system capable of receiving barrels from a variety of manufacturers rather than barrels specifically made for a particular type of receiver is particularly desirable.